Objective lens drive device, and optical pickup device using objective lens drive device

ABSTRACT

The present invention is relative with an objective lens driving device used in an optical pickup device, and includes a stationary unit, a lens bobbin provided with an objective lens, at least one magnet provided on one of the lens bobbin and the stationary unit, a coil unit provided on the other of the lens bobbin and the stationary unit for causing movement of the lens bobbin in a direction parallel to the optical axis of the objective lens and in a planar direction perpendicular to the optical axis of the objective lens, and an elastic supporting unit of a stainless material, provided between a stationary unit and the lens bobbin. The elastic supporting unit supports the lens bobbin for movement in a direction parallel to the optical axis of the objective lens and in a planar direction perpendicular to the optical axis of the objective lens.

TECHNICAL FIELD

[0001] This invention relates to an optical pickup device, used forwriting information signals on an optical recording medium, such as anoptical disc, and for reading out the information signals, recorded onthis recording medium, and to an objective lens driving device which maybe usefully applied to this optical pickup device.

BACKGROUND ART

[0002] An optical pickup device is routinely used for writinginformation signals on an optical recording medium, such as an opticaldisc, and for reading out the information signals recorded on thisrecording medium. This type of the optical pickup device includes a mainbody unit, provided with a light source, such as a semiconductor laser,and with a light receiving element, such as a photodiode, an objectivelens, on which falls a light beam radiated from the light source, and adriving mechanism for deflecting this objective lens in a presetdirection, which will be explained subsequently.

[0003] This objective lens driving mechanism supports an objective lens,adapted for converging the light beam, radiated from a light source,along a direction of the optical axis of the objective lens, that is inthe focusing direction, and along a direction perpendicular to theoptical axis, that is in the tracking direction, while causing theobjective lens to be deflected by an electromagnetic actuator in thefocusing and tracking directions. The objective lens driving mechanismcauses movement of this objective lens to be moved along the directionof the optical axis of the objective lens and along the directionperpendicular to the optical axis to cause a light spot formed by thisobjective lens on a signal recording surface of the optical recordingmedium to follow a recording track on the signal recording surface ofthe optical recording medium. That is, the objective lens drivingmechanism causes the objective lens to be moved along the direction ofthe optical axis of the objective lens, that is in the focusingdirection, to execute focusing control of converging the light beamradiated from the light source on the signal recording surface. Theobjective lens driving mechanism also causes the objective lens to bemoved in the focusing direction along the optical axis of the objectivelens, and in the tracking direction, that is in a directionperpendicular to the tangential line of the recording track, to cause alight converging point of the light beam radiated from the light sourceto follow the recording track, by way of performing tracking adjustment.

[0004] The objective lens driving mechanism includes a stationary unit,mounted on the main body unit, a lens bobbin, carrying the objectivelens, and a supporting member interconnecting the stationary unit andthe lens bobbin. The supporting unit is made up by four flexible finelinear members and supports the lens bobbin for movement along thedirection parallel to the optical axis and along the directionperpendicular to the optical axis with respect to the stationary unit.That is, each of the linear members making up the supporting unit hasits one end mounted on the stationary unit, while having its other endmounted on the lens bobbin.

[0005] The stationary unit is provided with a magnetic circuit unitcomprised of a magnet and a yoke. On the lens bobbin are mounted adriving coil for focusing and another driving coil for tracking, bothmounted in a magnetic field generated by a magnet constituting themagnetic circuit unit. In this objective lens driving mechanism, whenthe current is supplied to the driving coil for focusing, the drivingcoil for focusing is moved, along with the lens bobbin, along thedirection of the optical axis of the objective lens, together with thelens bobbin, under the interaction with the magnetic field generated bythe magnetic circuit unit. When the current is supplied to the drivingcoil for tracking, the driving coil for tracking is moved, along withthe lens bobbin, in the direction perpendicular to the optical axis ofthe objective lens, along with the lens bobbin, under the interactionwith the magnetic field generated by the magnetic circuit unit. By thisinteraction between the respective driving coils and the magneticcircuit unit, focusing control and tracking control are executed so thatthe light spot of the light beam radiated from the light source andconverged on the signal recording surface by the objective lens willfollow up with vertical movement of the signal recording surface andwith the recording track.

[0006] In this objective lens driving mechanism, current supply to therespective driving coils is via the respective linear members formingthe supporting unit. Consequently, these linear members are desirablyformed of a material which is low in electrical resistance and whichdoes not produce resonance in the frequency range used, for example,such a material as beryllium copper. Meanwhile, these linear members areof a thickness of the order of 80 μm, a width up to 80 to 90 μm and alength of the order of 15 to 20 mm.

[0007] In the above-described objective lens driving device, since thefour linear members forming the supporting unit are used as feeder linesfor the driving coil for focusing and for the driving coil for tracking,and hence need to be electrically independent of and electricallyinsulated from each other. Therefore, the linear members forming thesupporting unit must be formed as respectively separate members.

[0008] These linear members were difficult to form to high precision ina manner free from distortion or flexure. These linear members areformed by first punching a plate member, and by providing a unitcomprised of plural linear members 101, 101 lying within a frame-shapedframe 102, with the ends of the linear members being secured to theinner side edges of the frame 102, as shown in FIG. 1. The linearmembers 101, 101 then are severed from the frame 102. However, whensevered from the frame 102, the linear members 101 tend to be distortedor flexed.

[0009] It may be contemplated to interconnect both ends of the twolinear members 101, 101, neighboring to the objective lens drivingmechanism, by synthetic resin components 103, 103, by insert molding, asthe plural linear members 101, 101 are supported by the frame 102,thereby suppressing torsion or flexure of the linear members 101, 101.In this case, both ends of the two linear members 101, 101 are severedfrom the frame 102, as both ends of the linear members 101, 101 remainconnected to the synthetic resin components 103, 103. The resulting unitis used in this state as the objective lens driving device. If thelinear members 101, 101 are connected by the synthetic resin components103, 103 to the frame as described above, the resulting unit becomesthicker than the liner members per se. The unit carrying the linearmembers 101, 101 thus connected is locally different in thickness, sothat, if a plural number of such units are stacked directly together,the linear members 101, 101 tend to be deformed. For transporting theunits, carrying the linear members 101, 101, thus connected, in a stateof preventing the linear members 101 from becoming deformed, dedicatedpacking materials need to be used. If a large number of the units,carrying the linear members 101, 101, are to be packaged andtransported, the packages for transport, employing the dedicatedpackaging materials, are bulky in size, to render it impossible toimprove the transport efficiency.

[0010] Moreover, beryllium copper, retained to be convenient as amaterial forming the above-mentioned linear members, is difficult toprocure, while being costly.

DISCLOSURE OF THE INVENTION

[0011] It is therefore an object of the present invention to provide anobjective lens driving device, in which linear members supporting a lensbobbin may readily be formed, the supporting members may be packaged andtransported readily and in which the materials of the supporting memberscan be procured easily and manufactured inexpensively. It is anotherobject of the present invention to provide an optical pickup deviceemploying this objective lens driving device.

[0012] For accomplishing the above object, the present inventionprovides an objective lens driving device including a lens bobbinprovided with an objective lens, at least one magnet provided on thelens bobbin, a coil unit for causing movement of the lens bobbin alongwith the magnet in a direction parallel to the optical axis of theobjective lens and in a planar direction perpendicular to the opticalaxis of the objective lens, a stationary unit provided with the coilunit, and an elastic supporting unit of a stainless material, providedbetween the stationary unit and the lens bobbin; the elastic supportingunit supporting the lens bobbin for movement in a direction parallel tothe optical axis of the objective lens and in a planar directionperpendicular to the optical axis of the objective lens.

[0013] The elastic supporting unit includes a plurality of linearsupporting members each having its one end mounted to the lens bobbinand having its opposite end to the stationary unit.

[0014] The elastic supporting unit includes a first elastic supportingpart and a second elastic supporting part, each constructed as twoconnecting pieces, each of the connecting pieces interconnecting bothends of two of the plural supporting members so that the two supportingmembers extend parallel to each other.

[0015] The first and second elastic supporting parts are formed onpunching a stainless sheet material into a stainless plate member.

[0016] The stationary unit includes a plurality of grooves adapted forreceiving the opposite ends of the plural supporting members. In eachgroove, there is provided a damper in contact with the opposite end ofthe associated supporting member.

[0017] A substantially rectangular frame-shaped yoke is provided in thelens bobbin, two magnets are provided at a preset distance between twofacing inner wall sections of the yoke and wherein the coil unit isprovided between the magnets.

[0018] The present invention also provides an objective lens drivingdevice including a stationary unit, a lens bobbin provided with anobjective lens, at least one magnet provided on one of the lens bobbinand the stationary unit, a coil unit provided on the other of the lensbobbin and the stationary unit and adapted for supporting the lensbobbin for movement in a direction parallel to the optical axis of theobjective lens and in a planar direction perpendicular to the opticalaxis of the optical axis of the objective lens, and an elasticsupporting unit of a stainless material, provided between the stationaryunit and the lens bobbin; the elastic supporting unit supporting thelens bobbin for movement in a direction parallel to the optical axis ofthe objective lens and in a planar direction perpendicular to theoptical axis of the objective lens.

[0019] The present invention also provides an optical pickup deviceincluding a light source, an objective lens driving device, and aphotodetector for detecting the light beam incident thereon via theobjective lens. The objective lens driving device includes a lensbobbin, provided with an objective lens for converging a light beamradiated from the light source, a stationary unit having an opening forguiding the light beam radiated from the light source to the objectivelens, at least one magnet mounted on one of the lens bobbin and thestationary unit, a coil unit provided on the other of the lens bobbinand the stationary unit and adapted for causing movement of the lensbobbin in a direction parallel to the optical axis of the objective lensand in a planar direction perpendicular to the optical axis of theobjective lens, and an elastic supporting unit of a stainless materialprovided between the stationary unit and the lens bobbin for supportingthe lens bobbin for movement in a direction parallel to the optical axisof the objective lens and in a planar direction perpendicular to theoptical axis of the objective lens.

[0020] Other objects, features and advantages of the present inventionwill become more apparent from reading the embodiments of the presentinvention as shown in the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0021]FIG. 1 is a plan view showing a supporting member used for aconventional objective lens driving device.

[0022]FIG. 2 is a perspective view showing an objective lens drivingdevice according to the present invention.

[0023]FIG. 3 is an exploded perspective view showing the objective lensdriving device according to the present invention.

[0024]FIG. 4 is a plan view showing the objective lens driving deviceaccording to the present invention.

[0025]FIG. 5 is a side view thereof.

[0026]FIG. 6 is a front view thereof.

[0027]FIG. 7 is a plan view showing the status in the course ofmanufacturing a supporting member forming the objective lens drivingdevice.

[0028]FIG. 8 is a plan view showing the supporting member used in theobjective lens driving device according to the present invention.

[0029]FIG. 9 is a longitudinal cross-sectional view showing an opticalpickup device according to the present invention.

[0030]FIG. 10 is a graph showing oscillation characteristics of amovable unit of the objective lens driving device of the presentinvention in a direction parallel to the optical axis of the objectivelens.

[0031]FIG. 11 is a graph showing oscillation characteristics of themovable unit in a planar direction perpendicular to the optical axis ofthe objective lens.

[0032]FIG. 12 is a graph showing oscillation characteristics of amovable unit of a conventional objective lens driving device in adirection parallel to the optical axis of an objective lens.

[0033]FIG. 13 is a graph showing oscillation characteristics of themovable unit in a planar direction perpendicular to the optical axis ofthe objective lens.

BEST MODE FOR CARRYING OUT THE INVENTION

[0034] The present invention is now explained with reference to anembodiment thereof as applied to an objective lens driving device usedfor recording information signals on an optical disc as an opticalrecording medium and for reading out the information signals recorded onthe recording medium.

[0035] Referring to FIGS. 2 to 4, the objective lens driving deviceaccording to the present invention includes a base member 1, as astationary unit, a lens bobbin 3, carrying an objective lens 2, and foursupporting members 4 a, as an elastic supporting unit, interconnectingthe stationary unit and the lens bobbin.

[0036] The base member 1 is formed as a unitary member, from a syntheticresin material, as a substantially planar member. On the upper rearsurface of the base member 1, there are formed upright a supportingplate 5 and a pair of supporting pillars 6, 6. Between the supportingplate 5 and the supporting pillars 6, 6 is mounted a substantially flatmounting plate 7 with light press fitting. The mounting plate 7 ismounted in position by being introduced into a space between thesupporting plate 5 and the supporting pillars 6, 6. This mounting plate7 carries a pair of mounting arms 8, 8 on its both sides, as shown inFIG. 3. The mounting arms 8, 8 are formed as arms protruded on bothsides from the mounting plate 7, with the foremost flat parts thereofextending parallel to each other. At mid portions of the foremost flatparts of the mounting arms 8, 8 are formed positioning projections 9.

[0037] The supporting members 4 a are formed as fine flexible linearmembers, and support the lens bobbin 3 for movement in a directionindicated by arrow F and in a direction indicated by arrow T in FIG. 2with respect to the base member 1. That is, each supporting member 4 ahas its one end and its other end mounted on the base member 1 and onthe lens bobbin 3, respectively, as shown in FIGS. 2 to 4. The twosupporting members 4 a, lying in a direction parallel to the opticalaxis of the objective lens 2, are grouped together as a set and havetheir respective ends connected together by connecting pieces 10, 10.These supporting members 4 a are formed as one unitary unit from astainless material, as the supporting member 4 a run parallel to eachother and to the optical axis of the objective lens 2, as shown in FIG.3. That is, the two supporting members 4 a, 4 a and the two connectingpieces 10, 10 are punched respectively as one unit from a sheet of astainless material and are coupled together in a manner which will beexplained subsequently.

[0038] Each of the connecting pieces 10, 10 is formed at its mid portionwith a positioning hole 11. The positioning hole 11 of the connectingpiece 10 provided at one end is circular, while the positioning hole 11of the connecting piece 10 provided at the opposite end is an ellipticalhole having its long axis along the direction parallel to the supportingmembers 4 a. On both sides of the positioning hole 11 of each of theconnecting pieces 10, 10 is formed a pair of bonding holes 12, 12.

[0039] Referring to FIG. 3, the positioning projections 9 of themounting arms 8, 8 are inserted into the positioning holes 11 of theconnecting pieces 10, 10 on one side and an adhesive 13 is applied tothe bonding holes 12, 12 to secure the connecting pieces 10, 10 to theend faces of the mounting arms 8, 8 to secure elastic supporting units4, 4 to the end faces of the mounting arms 8, 8. At this time, thesupporting members 4 a, 4 a, 4 a, 4 a are supported in a cantileveredfashion for extending in a forward direction formed the mounting arms 8,8 over the lateral sides of the supporting plate 5, as shown in FIG. 2.The two elastic supporting units 4, 4 are mounted between the lensbobbin 3 and the supporting plate 5, on both sides of the objective lens2, so as to be parallel to each other, as shown in FIG. 2 or 4. With theconnecting pieces 10, 10 on one sides of the supporting members 4 a, 4 amounted to the mounting arms 8, 8 on both sides, the sum of foursupporting members 4 a, 4 a are carried by the respective mounting arms8, 8 for extending forwards in a cantilevered fashion over the lateralsides of the supporting plate 5, in a direction parallel to each other,as shown in FIG. 2.

[0040] In both lateral sides of the supporting plate 5 are formed upperand lower paired damper holding grooves 14, 14, as shown in FIGS. 2, 3and 5. The elastic supporting units 4, 4 are carried by the mountingarms 8, 8 through the damper holding grooves 14, 14 for extending in aforward direction, as shown in FIG. 2. In these damper holding grooves14, 14 are charged gelated dampers 15 formed of a silicon-basedmaterial. These dampers 15 are contacted with rim portions,specifically, one end portions, of the elastic supporting units 4, 4, asshown in FIG. 2. The result is that oscillation characteristics of amovable unit, including the lens bobbin 3, supported by this elasticsupporting units 4, 4, as later explained, are corrected by the dampers15.

[0041] The lens bobbin 3 is mounted on the connecting pieces 10, 10lying on the opposite side of the respective elastic supporting units 4,4. The lens bobbin 3, formed of a synthetic resin material, includes anobjective lens mounting hole 16, as a through-hole, as shown in FIG. 3.The lens bobbin 3 includes a yoke 17 formed of a high magneticpermeability material. In this objective lens mounting hole 16 ismounted the objective lens 2, such as an aspheric lens. The yoke 17 isformed as a rectangular frame, as shown in FIGS. 3 and 4, and is unifiedto the lens bobbin 3 by insert molding. In this lens bobbin 3, theobjective lens mounting hole 16 is provided at a mid portion of the lensbobbin 3, while the yoke 17 is positioned forwardly of the objectivelens mounting hole 16 of the lens bobbin 3, as shown in FIGS. 3 and 4.The lens bobbin 3 is provided with a pair of mounting surfaces 18, 18lying on both sides of the yoke 17. These mounting surfaces 18, 18 areplanar and formed so as to be parallel to each other. At mid portions ofthe respective mounting surfaces 18, 18 are formed positioningprotuberances 19, 19.

[0042] The elastic supporting units 4, 4 are mounted on the respectivemounting surfaces 18, 18, as shown in FIG. 2, as the positioningprotuberances 19, 19 provided on the mounting surfaces 18, 18 of thelens bobbin 3 are inserted into the positioning holes 11 of the oppositeside connecting pieces 10, 10, and as an adhesive 20 is subsequentlycoated and charged into the bonding holes 12, 12 for bonding theconnecting pieces 10, 10 and the mounting surfaces 18, 18 to each otherwith the adhesive 20. In this manner, the lens bobbin 3 is supported bythe four supporting members 4 a, 4 a, 4 a, 4 a. At this time, theobjective lens 2 is mounted so that its optical axis will beperpendicular to the upper surface of the base in member 1. At a midportion of the base member 1 in register with the so mounted objectivelens 2, there is bored a through-hole as an opening through which istransmitted the light beam so as to be incident on the objective lens 2.

[0043] The elastic supporting units 4, 4 are formed of stainlessmaterial and hence is flexible, so that it is movable in a focusingdirection which is parallel to the optical axis of the objective lens 2,as indicated by arrow F in FIG. 2, and in a planar tracking directionwhich is perpendicular to the optical axis of the objective lens 2, asindicated by arrow T in FIG. 2. When the lens bobbin 3 is moved in thismanner in the directions indicated by arrows F or T in FIG. 2, there isno risk of the optical axis of the objective lens 2 becoming tumbled ortilted, because the lens bobbin 3 is carried by the four supportingmembers 4 a.

[0044] The lens bobbin 3 is provided with a pair of magnets 21, 21forming a magnetic circuit unit in cooperation with the yoke 17. Themagnets 21, 21, forming the magnetic circuit unit, are each formed to arectangular shape, and are mounted by the inner wall section of the yoke17, formed to a rectangular frame shape, as described above, in a facingrelationship to each other via a preset gap, as shown in FIG. 3. Thesemagnets 21, 21 are mounted at a mid portion of the forward side innerwall section and at a mid portion of the rear side inner wall section,as shown in FIG. 4. By these magnets 21, 21 and the yoke 17, there isgenerated, at a mid portion within the inside of the yoke 17, that is ina spacing defined between the magnets 21, 21, a magnetic field in whichthe direction of the magnetic flux is along the forward and backwarddirection.

[0045] The lens bobbin 3, inclusive of the yoke 17, the objective lens 2mounted on this lens bobbin 3, the connecting pieces 10, 10, lying onthe opposite side of the elastic supporting units 4, 4, the adhesive 20and the magnets 21, 21, mounted on the yoke 17, make up a movable unitin the objective lens driving device.

[0046] The base member 1 carries focusing driving coils 22, 22 andtracking driving coils 23, 23, so that these coils will be located inthe magnetic field generated by the magnets 21, 21 forming theabove-mentioned magnetic circuit unit. The focusing driving coils 22, 22are each formed by winding an electrically conductive linear member inthe form of a horizontally elongated ellipse, while the tracking drivingcoils 23, 23 are each formed by winding an electrically conductivelinear member in the form of a longitudinally elongated ellipse. Thesefocusing driving coils 22, 22 and tracking driving coils 23, 23 arecarried at the respective lower sides in driving coil holding grooves 24formed in the upper surface of the base member 1, as shown in FIG. 3.The tracking driving coils 23, 23 are held side-by-side in the holdinggroove 24, while the focusing driving coils 22, 22 are held in theholding groove 24 for sandwiching the tracking driving coils 23, 23 fromthe forward and rear sides, as shown in FIGS. 2 to 4.

[0047] The focusing driving coils 22, 22 and the tracking driving coils23, 23 are introduced into the gap defined between the magnets 21, 21within the yoke 17 of the lens bobbin 3, in the form of a rectangularframe, as shown in FIG. 6. The upper horizontal linear portions of thefocusing driving coils 22, 22 and linear vertical portions of themutually adjacent sides of the tracking driving coils 23, 23 intersecteach other at the center within the inside of the yoke 17. Theintersecting portions of the focusing driving coils 22, 22 and thetracking driving coils 23, 23 are located in a spacing between themagnets 21, 21.

[0048] The base member 1 is provided with four terminals 25 held withinthe base member 1 and having foremost parts protruded forwards from thefront end thereof, as shown in FIG. 3. These terminals 25 are connectedto one ends of the focusing driving coils 22, 22, to opposite endsthereof, to one ends of the tracking driving coils 23, 23 and to theopposite ends thereof, by outlet lines, not shown. As a result, thefocusing servo signals and tracking servo signals are supplied asdriving signals to the focusing driving coils 22, 22 and trackingdriving coils 23, 23. The outlet lines are connected through the insideof the base member 1 to the respective terminals 25 and to therespective driving coils 22, 22 and 23, 23.

[0049] If, in the present objective lens driving device, the focusingservo signals are sent to the focusing driving coils 22, 22, theobjective lens 2 is moved, along with the lens bobbin 3, in the focusingdirection parallel to the optical axis of the objective lens 2, asindicated by arrow F in FIG. 6, under the interaction of the magneticfield generated by the magnets 21, 21 forming the magnetic circuit unitand that generated by the focusing driving coils 22, 22. If, in thisobjective lens driving device, the tracking servo signals are sent tothe tracking driving coils 23, 23, the objective lens 2 is moved, alongwith the lens bobbin 3, in the tracking direction perpendicular to theoptical axis of the objective lens 2, as indicated by arrow T in FIG. 6,under the interaction of the magnetic field generated by the magnets21,21 forming the magnetic circuit unit and that generated by thetracking driving coils 23, 23. This interaction between the respectivedriving coils 22, 23 and the magnetic circuit unit provides for focusingand tracking control in the optical pickup device as will be explainedsubsequently.

[0050] On the base member 1, a semi-cylindrical dust-proofing wallsection 28 is formed upright as one with the base member 1 forsurrounding the lens bobbin 3, outside its movement sphere, as shown inFIGS. 2, 3 and 4.

[0051] In the objective lens driving device of the present invention,driving signals are supplied to the respective driving coils not fromthe supporting members 4 a but from the terminals 25 via outlet lines,as described above. Thus, the supporting members 4 a do not have to beinsulated electrically from one another, but may be used as both endsthereof remain coupled to the connecting pieces 10, 10. Since there isno limitation to the materials making up the supporting members 4 a,insofar as the electrical resistance is concerned, any suitable materialthat is readily available, inexpensive and amenable to working, and thatis not subjected to resonant oscillations in the operating frequencyrange, may be used. The present objective lens driving device usesstainless material (chromium alloys), such as ‘SUS301’ or ‘SUS304’ asprescribed by JIS (Japan Industrial Standard) as such materialsatisfying the above requirements.

[0052] In forming the supporting members 4 a from such material, a platemember of stainless material, about 80 μm in thickness, as a rectangularframe 26, is formed on punching. The two supporting members 4 a, 4 a andthe connecting pieces 10, 10 on both ends of the supporting members 4 a,4 a are connected to the rectangular frame 26 via two straitenedportions 27, on each of both ends of the frame 26 within the boundariesof the rectangular frame 26, as shown in FIG. 7. The positioning holes11 and the bonding holes 12, 12 are simultaneously formed on punching.The straitened portions 27 of the member shown in FIG. 7 are cut tocomplete elastic supporting units 4, 4, having supporting members 4 a,both ends of which are interconnected by the connecting pieces 10, 10,as shown in FIG. 8.

[0053] The elastic supporting units 4, 4 remain connected at both endsby the connecting pieces 10, 10, even after disconnection from the frame26, and hence are not subjected to distortion or flexure. Depending onthe precision of a metal mold, used for punching, high precisionmachining may be achieved as to the pitch between the two supportingmembers 4 a, 4 a or the location of the positioning holes 11.

[0054] A large number of the elastic supporting units 4, still remainingconnected to the frames 26, may be stacked for packaging and transport.The elastic supporting units 4, 4, connected to the frame 26, are in theform of a flat sheet with a thickness on the order of 80 μm, are notbulky on being stacked, while being not liable to distortion. Since theeis no necessity of employing dedicated packaging materials, thetransport efficiency may be improved. Meanwhile, the elastic supportingunit 4, used in the present invention, is approximately 80 to 90 μm inwidth and approximately 15 to 20 mm in length.

[0055] As for oscillation characteristics of the movable unit of theoptical pickup device, the resonance frequency (f0) in a directionparallel to the optical axis of the objective lens 2 (FCS) is 29.5 Hz,as shown in FIG. 10, while the resonance frequency (f0) in the planardirection perpendicular to the optical axis of the objective lens 2 is27.0 Hz, as shown in FIG. 11, with the phase conditions also beingoptimum for both cases. As for the oscillation characteristics of anobjective lens driving device of a Comparative Example, having the samestructure as that described above, and in which the supporting member 4is formed of beryllium copper (an alloy of beryllium and coppercontaining not more than about 3% of beryllium), the resonance frequency(f0) in a direction parallel to the optical axis of the objective lens 2(FCS) is 31.7 Hz, as shown in FIG. 12, while the resonance frequency(f0) in the planar direction perpendicular to the optical axis of theobjective lens 2 (TRK) is 27.0 Hz, as shown in FIG. 13.

[0056] Thus, with the objective lens driving device of the presentinvention, employing a stainless material, as the material of thesupporting member 4, it is possible to achieve oscillationcharacteristics which are approximately equivalent to those of thedevice in which the supporting member is formed of beryllium copper. Theresults of our experiments have indicated that the stainless materialused as the material of the supporting member 4 as in the presentinvention is also equivalent to beryllium copper as to shock proofnessand durability.

[0057] The objective lens driving device of the present invention is notlimited to the above-described embodiments but may be constructed suchthat the magnetic circuit unit composed of the yoke and the magnet ismounted on the base member, with the focusing and tracking driving coilsthen being mounted on the lens bobbin. In such case, focusing controland tracking control may be achieved by the interaction between therespective driving coils and the magnetic circuit unit. In this case,the supporting members are not used as feeder lines for supplying thedriving signals to the respective driving coils and are formed ofstainless materials to realize optimum oscillation characteristics.

[0058] In the present objective lens driving device, the driving signalsare sent to the respective driving coils via a flexible substrateinterconnecting the lens bobbin and the base member. This flexiblesubstrate is formed by a base plate of, for example, polyimide resin,exhibiting flexibility and thermal resistance, and a preset electricallyconductive pattern formed thereon. The respective driving coils areconnected to the electrically conductive pattern on the flexiblesubstrate, and are fed with driving signals via the flexible substrate.

[0059] Referring to FIG. 9, the optical pickup device of the presentinvention includes a main body unit 30, on which is mounted the basemember 1 of the objective lens driving device described above. The basemember 1 is mounted on this main body unit 30 via set screws 31 threadedinto four tapped holes 29 provided at its four corners.

[0060] Within the main body unit 30 is enclosed a hologram laser device32, which is made up by substrate 35, carrying a semiconductor laserelement 33, as a light source, and a photodiode 34, as a light receivingelement, a hologram optical element 36, and a housing 37, having thesubstrate and the hologram optical element enclosed therein. Thehologram optical element 36 separates the light beam radiated from thesemiconductor laser element 33, from the light beam reflected back fromthe optical recording medium, as later explained, and outputs the lightreflected back from the optical recording medium towards the photodiode34.

[0061] With this optical pickup device, the light beam radiated from thesemiconductor laser element 33 is transmitted through the hologramoptical element 36 and through an astigmatism correction plate 38 so asto be radiated through an upper through-hole 39 formed in the uppersurface of the main body unit 30. The astigmatism correction plate 38 isa plan-parallel plate, arranged at an angle with respect to the opticalaxis of the light beam output from the semiconductor laser element 33,and corrects the astigmatism proper to the light beam transmittedtherethrough. The light beam radiated from the through-hole 39 of themain body unit 30 is transmitted through the through-hole formed in themid portion of the base member 1 to fall on the objective lens 2.

[0062] The light beam incident on the objective lens 2 is illuminated soas to be converged on a signal recording surface 105 of an opticalrecording medium 104, such as an optical disc. This light beam ismodulated as to strength or direction of polarization, depending on theinformation signals recorded on the signal recording surface 105, so asto be reflected by a reflection layer lined on the signal recordingsurface 105. The light beam reflected back from the reflection layer ofthe optical recording medium 104 is re-incident through the objectivelens 2 to the main body unit 30. The light beam reflected back from theoptical recording medium 104 falls on the hologram optical element 36through the astigmatism correction plate 36. In this hologram opticalelement 36, the light beam returned from the optical recording medium104 is deflected with respect to the optical return path to thesemiconductor laser 36 to fall on the photodiode 34.

[0063] The photodiode 34 receives the reflected light from the opticalrecording medium 104, deflected by the hologram optical element 36, tooutput electrical signals corresponding to the state of modulation inthis light beam. It is possible to generate readout signals of theinformation signals, recorded on the optical recording medium 104, basedon the output signal of the photodiode 34. From the output signal of thephotodiode 34, focusing error signals and tracking error signals aregenerated by an error signal generating circuit. Based on the sogenerated focusing error signals and tracking error signals, focusingservo and tracking servo signals are generated by the servo circuit. Theso generated focusing servo and tracking servo signals are sent to thefocusing driving coils 22, 22 and to the tracking driving coils 23, 23,as described above.

[0064] In this optical pickup device, the objective lens driving devicecauses movement of the objective lens 2, by the respective driving coils22, 23 and the maginetic circuit unit, in the focusing directionparallel to the optical axis of the objective lens 2 and in the planartracking direction perpendicular to this optical axis, such as to causethe light converging point of the light beam from the semiconductorlaser device 32 to follow a recording track on the signal recordingsurface 105 of the optical recording medium 104 by the objective lens 2.

[0065] That is, in the present objective lens driving device, theobjective lens 2 is moved in a direction parallel to the optical axis ofthe objective lens 2 to cause the light beam radiated from thesemiconductor laser device 33 as the light source to follow theup-and-down movement of the optical recording medium 104 so as to beconverged on the signal recording surface 105 by way of focusingcontrol. In this objective lens driving device, the objective lens 2 isalso moved in a direction perpendicular to a tangential line drawn to arecording track in the planar direction orthogonal to the optical axisof the objective lens 2 to cause the light converging point of the lightbeam radiated from the semiconductor laser device 33 as the light sourceto follow up with eccentricities of the optical recording medium 104 soas to follow the recording track by way of tracking control.

[0066] In the above-described focusing control and tracking control, thefocusing error signals corresponding to the distance between the lightbeam converging point and the signal recording surface 105, and thetracking error signals corresponding to the distance between the lightbeam converging point and the recording track, are generated, based onthe output signal from the photodiode 34. The focusing servo signals andthe tracking servo signals are sent as driving signals to the focusingdriving coils 22, 22 and to the tracking driving coils 23, 23, based onthese focusing error signals and tracking error signals.

[0067] Industrial Applicability

[0068] With the above-described objective lens driving device, accordingto the present invention, in which the power can be supplied to thedriving coils without employing the supporting members, adapted formovably supporting the lens bobbin, as feeder lines for the drivingcoils, it becomes possible to formed the supporting members of astainless material, to enlarge the gamut for the selection of thematerials used for forming the supporting members and to realize optimumoscillation performance required of the objective lens driving device.

[0069] Since the gamut for the selection of the materials for thesupporting members, is now wider, it becomes possible to use a stainlessmaterial, which is less costly than other metals, to render it possibleto manufacture the apparatus itself inexpensively.

[0070] That is, with the present invention, such an objective lensdriving device may be provided in which linear supporting members,supporting the lens bobbin, can be formed easily, the supporting memberscan be packaged and transported easily and in which the materials of thesupporting members are readily available and inexpensive.

1. An objective lens driving device comprising: a lens bobbin providedwith an objective lens; at least one magnet provided on said lensbobbin; a coil unit for causing movement of said lens bobbin along withsaid magnet in a direction parallel to the optical axis of the objectivelens and in a planar direction perpendicular to the optical axis of theobjective lens; a stationary unit provided with said coil unit; and anelastic supporting unit of a stainless material, provided between saidstationary unit and the lens bobbin; said elastic supporting unitsupporting said lens bobbin for movement in a direction parallel to theoptical axis of said objective lens and in a planar directionperpendicular to the optical axis of said objective lens.
 2. Theobjective lens driving device according to claim 1 wherein said elasticsupporting unit includes a plurality of linear supporting members eachhaving its one end mounted to said lens bobbin and having its oppositeend to said stationary unit.
 3. The objective lens driving deviceaccording to claim 2 wherein said elastic supporting unit includes afirst elastic supporting part and a second elastic supporting part, eachconstructed as two connecting pieces, each of said connecting piecesinterconnecting both ends of two of said plural supporting members sothat said two supporting members extend parallel to each other.
 4. Theobjective lens driving device according to claim 3 wherein said firstand second elastic supporting parts are formed on punching a stainlesssheet material into a stainless plate member.
 5. The objective lensdriving device according to claim 3 wherein said first and secondelastic supporting parts are arranged parallel to each other on bothsides of said objective lens with said objective lens in-between.
 6. Theobjective lens driving device according to claim 2 wherein saidstationary unit has a plurality of grooves for receiving the oppositeends of said linear supporting members, and wherein a damper is providedin each groove in contact with the opposite end of the associated linearsupporting member.
 7. The objective lens driving device according toclaim 1 wherein a substantially rectangular frame-shaped yoke isprovided in said lens bobbin, two magnets are provided at a presetdistance between two facing inner wall sections of said yoke and whereinsaid coil unit is provided between said magnets.
 8. An objective lensdriving device comprising: a stationary unit; a lens bobbin providedwith an objective lens; at least one magnet provided on one of said lensbobbin and the stationary unit; a coil unit provided on the other ofsaid lens bobbin and the stationary unit and adapted for supporting saidlens bobbin for movement in a direction parallel to the optical axis ofsaid objective lens and in a planar direction perpendicular to theoptical axis of said optical axis of said objective lens; and an elasticsupporting unit of a stainless material, provided between saidstationary unit and the lens bobbin; said elastic supporting unitsupporting said lens bobbin for movement in a direction parallel to theoptical axis of said objective lens and in a planar directionperpendicular to the optical axis of said objective lens.
 9. Theobjective lens driving device according to claim 8 wherein said elasticsupporting unit includes a plurality of linear supporting members eachhaving its one end mounted to said lens bobbin and having its oppositeend to said stationary unit.
 10. The objective lens driving deviceaccording to claim 9 wherein said elastic supporting unit includes afirst elastic supporting part and a second elastic supporting part, eachconstructed as two connecting pieces, each of said connecting piecesinterconnecting both ends of two of said plural supporting members sothat said two supporting members extend parallel to each other.
 11. Theobjective lens driving device according to claim 10 wherein said firstand second elastic supporting parts are formed on punching a stainlesssheet material into a stainless plate member.
 12. The objective lensdriving device according to claim 10 wherein said first and secondelastic supporting parts are arranged parallel to each other on bothsides of said objective lens with said objective lens in-between. 13.The objective lens driving device according to claim 9 wherein saidstationary unit has a plurality of grooves for receiving the oppositeends of said linear supporting members, and wherein a damper is providedin each groove in contact with the opposite end of the associated linearsupporting member.
 14. An optical pickup device comprising: a lightsource; an objective lens driving device; said objective lens drivingdevice including a lens bobbin, provided with an objective lens forconverging a light beam radiated from said light source; a stationaryunit having an opening for guiding the light beam radiated from saidlight source to said objective lens; at least one magnet mounted on oneof said lens bobbin and said stationary unit; a coil unit provided onthe other of said lens bobbin and said stationary unit and adapted forcausing movement of said lens bobbin in a direction parallel to theoptical axis of said objective lens and in a planar directionperpendicular to the optical axis of said objective lens; and an elasticsupporting unit of a stainless material provided between said stationaryunit and the lens bobbin for supporting said lens bobbin for movement ina direction parallel to the optical axis of said objective lens and in aplanar direction perpendicular to the optical axis of said objectivelens; and a photodetector for detecting the light beam incident thereonvia said objective lens.
 15. The optical pickup device according toclaim 14 wherein said elastic supporting unit includes a plurality oflinear supporting members each having its one end mounted to said lensbobbin and having its opposite end to said stationary unit.
 16. Theobjective lens driving device according to claim 15 wherein said elasticsupporting unit includes a first elastic supporting part and a secondelastic supporting part, each constructed as two connecting pieces, eachof said connecting pieces interconnecting both ends of two of saidplural supporting members so that said two supporting members extendparallel to each other.
 17. The objective lens driving device accordingto claim 16 wherein said first and second elastic supporting pieces areformed on punching a stainless sheet material into a stainless platemember.
 18. The objective lens driving device according to claim 16wherein said first and second elastic supporting pieces are arrangedparallel to each other on both sides of said objective lens with saidobjective lens in-between.
 19. The objective lens driving deviceaccording to claim 15 wherein said stationary unit has a plurality ofgrooves for receiving the opposite ends of said linear supportingmembers, and wherein a damper is provided in each groove in contact withthe opposite end of the associated linear supporting members.